Does it have to be during the week? That makes it difficult (tho not impossible). Fridays would be the best week day, weekends would be easiest for me.
People coming up from the south could always stay over at mine and get a lift to Hull with me (you don't mind doing the water changes for me do ya?). Ditto northern folk who want to go to London but would be too much travelling in one go. Grantham seems fairly central, and I have some spare bed/sofa/floor space as long you don't mind sharing with the cats!